Method of manufacturing a filter cartridge

ABSTRACT

An injection moulding assembly includes a male moulding member surrounded by a female moulding member forming a void between them that upon injection of molten plastics into the mould a container can be formed. The moulding assembly includes a guide rod and ejection flange and a pair of ejection flange guide rods, an air vent valve and an injection passage. The male member includes in this embodiment eight grooves unevenly spaced so that the partially hardened container formed in the injection mould can be pushed from the mould using the ejection flange while the container is sufficiently green to enable the ribs formed in the grooves to move over the surface of the male mould during the ejection process.

This application is a division of application Ser. No. 09/868,333, filedon Jun. 18, 2001, application Ser. No. 09/868,333 is the national phaseof PCT International Application No. PCT/AU99/01121 filed on Dec. 17,1999 under 35 U.S.C. §371. The entire contents of each of theabove-identified applications are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to filtration and in particular but not limitedto filtration of engine, transmission and hydraulic oils, fuel andsolvents.

BACKGROUND ART

Oil filtration involves the use of full flow filters that filter all oilon every pass through the filter and the use of by-pass oil filters inconjunction with the full flow filters. By-pass oil filters operate inparallel with the full flow filter and generally speaking have a greaterfiltration than the full flow filter.

Full flow elements filter all oil on every pass and work using anelement operating like a series of small sieves, with tiny holesallowing oil to pass through, while filtering out particles too large topass through the sieve-like element. However, the holes are not smallenough to filter out many finer particles, and it is these particlesthat can cause significant engine wear over a period of time.

On the other hand a by-pass filter operates in parallel with the fullflow filter and can be much finer to progressively remove finercontaminants not captured by the full flow filter. The use of a by-passfilter progressively filters all the oil, thus increasing the usefullife of the oil and reducing engine wear.

Typical by-pass oil filters include pleated element by-pass elements.These filters employ a longitudinally pleated membrane that is prone tobecome clogged after just a few hours work. Many by-pass filters have apressure release valve that opens when this occurs. Another type ofby-pass filter is a multiple disc by-pass filter which lasts much longerthan the pleated elements.

The most effective by-pass filters employ a roll of paper wound on acentral core with the feedstock being forced edgewise through the rollof paper to progress longitudinally the full width of the paper media.The filtrate then flows to the central core where it exits the filtervia a return pipe. The principle of operation of this type of filter isdifferent to the sieve-like filter and the pleated filter in so far asthe paper roll filter relies on oil passing between the layers of paper,instead of passing through a sieve-like element.

Early forms of paper roll filters employed a toilet roll fitted within afilter housing. Later more sophisticated forms employed a filter elementcomprising a disposable canister holding the paper roll.

Australian patent number 650176 describes a filter element of thecartridge type employing a filter housing with a filter element withinthe housing. The filter element employs a metal canister with a paperroll forced into the canister under pressure, the canister being open atone end, for entry of feedstock, with a base at the other end, the basehaving a central hole for the return pipe. A layer of gauze in the baseof the canister allows the filtrate to flow across the base to thereturn pipe in the central core. The sides of the canister are ribbed toinhibit feed stock tracking down the sides of the canister. The canisteralso has three or four depressions circumferentially spaced depressionsin the base to hold the gauze layer away from the base providing clearsecondary flow passages below the gauze to improve flow of filtrate.

The paper is tightly wound providing a much finer effective filter thanthe pleated and disc type filters.

Nevertheless the metal canister has a number of disadvantages. Theribbed side wall is employed to inhibit tracking of feedstock down theside wall outside the filter media but limits the density of the media.While ribbing is effective to limit tracking the canister is prone tobuckle under load while the paper is being pressed into the canister.This effectively limits the amount of sideways compression that can beapplied to the paper roll to a maximum defined by the flex in the sidewalls of the can and the inherent flexing of the ribs as the paper isbeing pushed into position, the limit being canister failure.

The element construction of Australian patent number 650176 results in afive percent (5%) failure rate of canisters during insertion of thepaper roll into the canisters. Also the canisters are prone to becrushed by oil pressure when in use particularly at cold start up whenthe oil is most viscous. Construction of canisters from thicker metalwould make filters more expensive and the ribbing to prevent trackingmore difficult to produce in a technical sense.

Since the metal canisters are disposable they must be designed forsingle use application at a reasonably economical cost. It would bedesirable to provide an alternative that is competitively priced,improves filtration and is less likely to buckle under load.

As an alternative to metal canisters PCT/AU96/00762 describes a plasticsfilter canister suitable for repeated use to enable recycling of thecanister. The canister is made sufficiently rigid such that the spentpaper roll can be removed using a tool and a fresh roll inserted intothe canister. Due to the construction of the metal canisters of patentnumber 650176 efforts to remove the spent rolls from the metal canisterswould in most cases render the metal canisters unusable having beendesigned for use as a disposable element. The problem with the canisterdescribed in. PCT/AU96/00762 is that the design is not amenable to massproduction using injection moulding techniques. In addition, the base ofthe canister was designed with closely spaced concentric rings in aneffort to reproduce the effect of the secondary flow through passagesutilized in the base of the metal canister while supporting the media.While this arrangement was effective in supporting the filter media andgauze the flow characteristics were less than desirable.

OUTLINE OF THE INVENTION

The present invention achieves its objectives to provide an improveddisposable or reusable canister by providing a rigid plastics canisterholding a roll of filter paper under higher sideways compression thanknown in the prior art while enabling manufacture of the filter canisteras a one piece injection moulded canister.

In one aspect therefore the present invention resides in a method forconstruction of an internally ribbed injection moulded hollow tubesection suitable for use in a filter element holding a paper roll filtermedia, the method comprising the steps of:

(i) providing a generally cylindrical male mould member havinglongitudinally spaced rib defining grooves;

(ii) providing a female mould member adapted to overlay the male mouldmember in closely spaced relation defining a tube shaped void betweenthe mould members;

(iii) injecting moulding material into the void, said moulding materialbeing selected to provide a substantially rigid tube when cured;

(iv) removing the female mould member from the male mould member whilethe tube is in a green state, the grooves in the male mould memberretaining the tube in position on the male mould member; and

(v) subsequently forcing the tube from the male mould member while thetube is still in a green state.

The term “green state” is used herein to mean a condition of hardeningwhereby the dimensions of the grooves and the degree of hardening of thetube is such that the moulded tube ribs can be pushed from the groovesin the male member without significant distortion of the tube comparedto a higher degree of hardening whereby the grooves serve to retain thetube on the male member.

The timing of the release of the tube from the male member will dependupon the nature and characteristics of the plastics moulding materialused.

It is desirable that the grooves are not uniformly spaced on the malemember so that once the initial release of the tube from all the groovesat the first instance takes place as the tube is slid over the malemember, the ribs do not all encounter grooves at the same time. Thus,due to the selected uneven spacing of the grooves, the force required topush the tube over the grooves is restricted such that as the tube ispushed off less than the full complement of ribs engage the grooves atany one time during the process whereby the tube is pushed from the malemember.

The tube can be open ended or can have one end closed. The tubetypically has open ends when it is intended to form an outer casing fora double ended filter such as a fuel filter.

Where the mould includes a void at the free end of the male member forforming a transverse base across one end of the tube, during productionand while the moulding material covers the free end of the male memberit is preferable to vent the inside of the base through the male memberto avoid suction that may inhibit the pushing of the tube off the malemember.

In another aspect the invention resides in a rigid injection mouldedgenerally cylindrical canister, the canister having a side wall, theside wall having an outer surface and an inner surface, the canisterbeing used as a filter element holding a paper roll as filter media, thecanister having a thin side wall and there being spaced anti-trackingribs projecting from the inner surface of the side wall and projecting adistance sufficient to enable the canister to be removed from a malemould member defining said ribs, the paper roll being of marginallygreater diameter than the internal diameter of the canister, thecanister being sufficiently rigid and the paper roll being sufficientlytightly wound that the paper roll when inserted into the canister usinga press is substantially compressed to the internal dimensions of thecanister without distortion of the canister.

Typically, the assembled filter element is employed in a standard filterhousing where the external dimensions of the element is about 110 mm indiameter and 170 mm long, the applicant has found that using 17 gsmthick paper and paper a paper density above about 15 m/cm radial widthreduces flow to undesirable levels whereas densities of about 13 m/cmradial width is optimum for maximising filtration but at the same timemaintaining desirable flow rates, densities below about 11 m/cm radialwidth the roll tends to collapse within the canister base flow canbecome blocked and the anti-tracking ribs become ineffective. Althoughfilters do work for a short time at these lower densities effective andreliable filtration generally occurs above about 12 m/radial cm. Thepresent invention in this preferred form enables just the right amountof paper, matched to the rib size and most desirable compression suitedto injection moulding and reliable in operation when compared to theprior art.

Preferably the side walls of the canister include marginal flaring of atleast one end of the canister so that the side wall of the canister ismedially biased of the order of 0.5 to 1 millimeter so that the sidewall of the canister is biased inwardly to resist distortion of the sidewall and enhance compression of the paper roll inside the canister.Typically the flared end is the open end at which the paper roll ispushed into the canister.

Preferably the ribs project 1 millimeter to 2 millimeters from the innersurface of the canister with 1.5 millimeters being optimum. Where theribs are evenly spaced it is preferable that they be at the shallowerend of the range of projection, the inner wall may have a slight taperon the inner surface to further assist release from the male mould.However, the paper must be more tightly wound and placed under highercompression to achieve the same filter efficiency and anti-tracking whencompared to a cylindrical shape where the inner diameter is uniform orcarries the medially biased inward shape.

The canister preferably includes a marginal taper on the inner surfaceat the open end to act as a lead in for the paper roll, the objectivebeing to minimise the “give” in the canister and to maximise thesideways compression applied to the shallow anti-tracking ribs.

Preferably where the canister has a base, the base includes externalradial strengthening ribs and again is biased inwardly. The base istypically inwardly dished by up to 2 millimeters at the centre relativeto the edges in order to provide a bias against the loading of the paperroll as the paper roll is being pressed home into the canister.

The base preferably has an inner surface with radially extending flowpassages separated by lands, the lands defining supporting surfaces fora gauze to evenly distribute and support the paper roll media across thebase of the canister and to provide secondary flow passages across thebase of the canister below the gauze.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention can be more readily understood andbe put into practical effect reference will now be made to theaccompanying drawings which illustrate preferred embodiments of theinvention and wherein:

FIG. 1 is a drawing illustrating an injection moulding apparatus forimplementing the method described;

FIGS. 2, 3 and 4 are schematic drawings illustrating the mouldingprocess utilising the apparatus of FIG. 1;

FIGS. 5 and 6 are opposite perspective views;

FIG. 7 is a top view;

FIG. 8 is a bottom view; and

FIG. 9 is a cross-section all illustrating a canister made using theapparatus of FIG. 1;

FIG. 10 is a perspective drawing illustrating a hydraulic press used topush a paper roll into the canister of FIGS. 5 to 9;

FIG. 11 is a schematic drawing illustrating operation of the press andthe assembly of an oil filter element;

FIG. 12 is a schematic drawing of the hydraulic circuit for the press;and

FIG. 13 is a section through a fuel filter element.

METHOD OF PERFORMANCE

Referring to the drawings and initially to FIG. 1 there is illustratedan injection moulding assembly 10 comprising a male moulding member 11surrounded by a female moulding member 12 forming a void 13 between themthat upon injection of molten plastics into the mould a container can beformed. The moulding assembly includes a guide rod 14 and ejectionflange 16 and a pair of ejection flange guide rods 17 and 18, an airvent valve 15 and an injection passage 19. The male member 11 includesin this embodiment eight grooves 20 unevenly spaced so that thepartially hardened container formed in the injection mould can be pushedfrom the mould using the ejection flange 16 while the container issufficiently green to enable the ribs formed in the grooves 20 to moveover the surface of the male mould 11 during the ejection process.

FIGS. 2, 3 and 4 illustrate the three stages of production of acontainer using the injecting moulding assembly of FIG. 1. FIG. 2represents the first stage in the process whereby liquid plastic isforced in under pressure and is represented as the black section at 21.An air vent valve at 15 is closed and the female moulding member 12 isin the closed position along the main guide rails 22.

In stage 2 represented by FIG. 3 the female mould member 12 has beenwithdrawn while the container 23 remains on the male moulding member.The container 23 is still green at this stage. In the third stage of theprocess the ejection flange 16 is driven along the surface of the malemould member and the air vent valving is opened and the container 23 ispushed off the male moulding member 11 as illustrated in FIG. 4.

A typical container formed using the apparatus of FIG. 1 is illustratedin FIGS. 5 to 9. The container is a generally cylindrical canisterhaving a side wall 24, the side wall having an outer surface 25 and aninner surface 26, the canister being used as a filter element holding apaper roll as filter media, the canister has a thin side wall andincludes spaced anti-tracking ribs 27 that project in this case 1.5millimeters into the interior of the container. The base 28 is inwardlydished at 29 and also includes a curved seat 30 for a sealing washer, asingle aperture 31 being provided for a return tube for returning thefiltrate from the filter to the main oil or fuel circuit. The base isexternally ribbed with strengthening ribs 32 while the interior of thebase includes radial flow passages 33 separated by lands 34. As can beseen there are in this embodiment 18 flow passages 33 and an annularprojection 35. The annular projection 35 also serves an anti-trackingpurpose in so far as any small amounts of oil that begin to track downthe sides of the container become trapped in the annular channel 63around the base 28 of the canister. The container 23 includes a flaredmarginal edge region at 36 and an outward chamfer at 37 which operatesas a lead in for the paper roll into the canister 23.

FIG. 10 illustrates the operation of a press 38 employing a hydraulicram 39 having a cylinder assembly 40 with a piston rod 41 and a baseplaten 43 with a control valve 44.

Assembly of a filter element is illustrated in FIG. 11. The diametersillustrated with the arrows 45 and 46 are approximately the same withthe paper roll 47 comprising approximately 43 meters of paper wound intoa tight 110 millimeter to 114 millimeter diameter roll on a cardboardcore 48.

A layer of gauze 49 is placed in the base of the canister 23, the paperis initially pushed into position by hand as illustrated in FIG. 10 andthen the guiding platen 42 is placed down onto the paper roll,activation of the hydraulic cylinder assembly causes the paper roll tobe pushed into the canister 23.

The press used to force the paper roll into the canister in one typicalembodiment is a 50 millimeter diameter hydraulic cylinder assembly 39. Aone horse power single phase electric motor drives a 20 liter per minutegear pump 50. The cylinder operating pressure is 70 to 80 pounds persquare inch which is achieved through an in-built adjustable reliefvalve 51. The relief valve is situated at the directional spool valvethat the operator uses to operate the cylinder 52.

Other elements illustrated in the hydraulic circuit is the hydraulicreservoir 53 and a pressure valve 54 and a filter 55.

The last drawing illustrates application of the present invention to afuel filter element 56 which can be made using the apparatus of FIG. 1simply by adjusting the thickness of the base to be very thin so thatthe base can be removed making an open ended tube. Fuel to be filteredflows into the tube from both ends. Two half size paper rolls 57, 58 areinserted with a return flow path provided by an intermediate gauze 59. Areturn tube 60 is located in the central core as in the previousembodiment.

Whilst the above has been given by way of illustrative example of thepresent invention many variations and modifications thereto will beapparent to those skilled in the art without departing from the broadambit and scope of the invention as herein set out in the appendedclaims.

1. A method of constructing an internally ribbed injection molded hollowtube for a filter element, the method comprising steps of: providing agenerally cylindrical male mold member having longitudinally spaced ribsdefining grooves and a free end; providing a female mold member adaptedto overlay the male mould member in closely spaced relation and define atube shaped void between the mold members; injecting molding materialinto the void, said molding material providing a solid-walledsubstantially rigid tube when cured; removing the female mold memberfrom the male mold member while the tube is in a green state, thegrooves in the male mould member retaining the tube in position on themale mould member; and subsequently forcing the tube from the male moldmember while the tube is still in a green state to form an internallyribbed injection molded solid-walled hollow tube having an open end,wherein the grooves are not uniformly spaced on the male mold member andfurther comprising the step of progressively sliding the tube off themale mold member, so that once the initial release of the tube from allof the grooves takes place, ribs formed in the grooves do not allencounter grooves at the same time.
 2. The method according to claim 1,wherein the tube shaped void includes a void forming a transverse baseacross one end of the tube at the free end of the male mold member, andfurther comprising the step of opening valving to vent the inside of thebase through the male mold member to avoid suction that may inhibitpushing of the tube off the male mold member.
 3. The method according toclaim 2, wherein the base is inwardly biased.
 4. The method according toclaim 2, wherein the base is inwardly dished at a center thereofrelative to edges of the base in order to provide a bias, a paper rollis being pressed into the hollow tube.
 5. The method according to claim2, wherein the base has an inner surface with radially extending flowpassages separated by lands, and further comprising the step ofinserting a paper roll media into the hollow tube, the lands defining asupporting surface to evenly distribute and support the paper roll mediaacross the base of the hollow tube to provide secondary flow passagesacross the base of the hollow tube.
 6. The method according to claim 1,further comprising the step of inserting a filter element holding apaper roll as filter media into the open end of the hollow tube using apress, the paper roll being of marginally greater diameter than theinternal diameter of the hollow tube and the hollow tube beingsufficiently rigid and the paper roll being sufficiently tightly woundthat the paper roll is substantially compressed to the internaldimension of the hollow tube without distortion of the hollow tube. 7.The method according to claim 1, wherein ribs formed in the groovesproject at 1 mm to 2 mm from an inner surface of the hollow tube.
 8. Themethod according to claim 7, wherein the ribs project about 1.5 mm fromthe inner surface of the hollow tube.
 9. The method according to claim1, wherein the hollow tube includes a marginal taper on an inner surfacethereof, at the open end to act as a lead-in for a paper roll.